What you’re running into is the difference between IMAP and POP3 in TB. If your account is set up as IMAP, Thunderbird is syncing with Yahoo in real time.

That means if you delete a message on Yahoo’s server (or from Thunderbird), it gets deleted everywhere. IMAP is designed for synchronization, not long-term local storage.

Solution: We can try to Switch you to POP3 instead

• POP3 downloads messages to your computer and (if you choose) removes them from the Yahoo server.

• In Thunderbird, you’d need to remove your IMAP account and re-add the Yahoo account using the POP3 option.

• Once set, your emails will live locally on your computer in Thunderbird’s profile folder. Deleting them from Yahoo afterward won’t affect your Thunderbird copies.

Another approach is to create local folders in Thunderbird and move your messages to them. I would not switch to POP because of the trade-offs. IMAP is much better for me and for many users.

Nice. Thanks for your replies. I suppose I should be more detailed. I want to save my 20 year plus yahoo emails just because I occasionally reference things from them. I don't mind using yahoo but would like to cut out 3/4 of the old stuff so yahoo is happy. Then I could open TB when I need to find an old email. Does that make sense? Or should I be using these modern tools a different way?

Also I guess I don't know are the emails physically stored on my hard drive with TB? I would have thought so but the "Profiles" folder is only 159MB. I already moved the "Profiles" folder to a 1T hard drive.

I'm going to tell you what to do if you want to keep messages in local folders. If you want to use a POP account instead of an IMAP account, ThundaMike or someone else will have to help you. To help you decide:

https://support.mozilla.org/en-US/kb/difference-between-imap-and-pop3

I want to save my 20 year plus yahoo emails just because I occasionally reference things from them. I don't mind using yahoo but would like to cut out 3/4 of the old stuff so yahoo is happy. Then I could open TB when I need to find an old email. Does that make sense? Or should I be using these modern tools a different way?

It makes sense and it is a good way to use Thunderbird.

Also I guess I don't know are the emails physically stored on my hard drive with TB? I would have thought so but the "Profiles" folder is only 159MB.

I am guessing that you have not told Thunderbird to download all your messages. The Yahoo server has all your messages, but Thunderbird does not. For every folder, the messages of which you want to preserve:

1. Right-click on the folder in Thunderbird and select "Properties".
2. Click on the "General Information" tab and check "When getting new messages for this account, always check this folder".
3. Click on the "Synchronization" tab.
4. Check "Select this folder for offline use".
5. Click on "Download Now".
6. Click on "OK".
7. Confirm that all the messages were downloaded and that your profile is about the size that you expect it to be.

Another possibility is that you did not actually select your profile folder when you copied or moved it. If you are not sure that you did:

1. In the "Help" menu, click on "Troubleshooting information ...".
2. Click on "about:profiles".
3. Find your current profile and the row with its root directory.
4. Click on "Show [varies by operating system]".
5. The folder selected in your computer's file system is the one that you want to copy.

I already moved the "Profiles" folder to a 1T hard drive.

Did you really move it or copy it? I hope that you copied it. Was your purpose to create a back-up copy of your profile? That is a good thing to do. You'll want to make sure that Thunderbird has all your messages before you do that. See above.

Now, to store your messages in Thunderbird but not in Yahoo:

1. Make sure that Thunderbird has all my messages. See above.
2. Make a back-up copy of your profile.
3. Create local folders in Thunderbird for long-term storage of your messages.
4. Folder-by-folder, copy messages from the server folders to the local folders. Wait for the sync with the server to finish. If you have reached a storage limit at Yahoo, sync could take a long time.
5. Folder-by-folder, confirm that all the messages were copied.
6. Make another back-up copy of your profile. Do not write over the first one.
7. At the server, delete all the folders whose messages were copied or that you don't want to keep. I don't know if Yahoo will "permanently delete" the folders in one step or move them to the trash folder. If it moves them to the trash folder, empty the trash. Wait for the sync with Thunderbird to finish.
8. Confirm that the folders and messages that you wanted to delete are deleted from Thunderbird.
9. Make another back-up copy of your profile.

Thank you Rick for the detailed info! I'm thinking this may be beyond my understanding? Did you second set of steps and I see my Profile is still on my internal drive (which I guess was default location upon installing Thunderbird). I have no room on my internal so I looked through these questions/forum on how to move to the external. Which I don't think worked.

Currently internal profile is 7GB (should be 20GB). External profile is 180MG.

Can I set the Root and Local to the external? Then do you first set of step:

   " Right-click on the folder in Thunderbird and select "Properties".
   Click on the "General Information" tab and check "When getting new messages for this account, always check this folder".
   Click on the "Synchronization" tab.
   Check "Select this folder for offline use".
   Click on "Download Now".
   Click on "OK".
   Confirm that all the messages were downloaded and that your profile is about the size that you expect it to be. "

If the profile on your internal drive is seven GB and its copy on the external drive is 180 MB, you must not have copied the profile.

Try again.

1. In the "Help" menu, click on "Troubleshooting information ...".
2. Click on "about:profiles".
3. Find your current profile and the row with its root directory.
4. Click on "Show [varies by operating system]".
5. The folder selected in your computer's file system is the one that you want to copy.

Perhaps in step 3 last time, you had the wrong row. Make sure you click on "Show ..." in the row of the *root* directory.

Compare the size of the copy with the size of the orginal to confirm success.

After you have copied your profile, see here for how to tell Thunderbird that you want to use that instance of your profile: https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data#w_moving-a-profile

Then we can proceed with getting messages out of Yahoo and into the profile on your external drive.